1. Field of the Invention
This invention relates to paving machines, and in particular to the provision of a completely automated paving machine capable of high speed paving over almost any type or condition of subgrade, including when variations in widths are encountered.
2. Description of the Prior Art
The type of paving machine to which this invention relates is generally characterized by a frame which is supported on and is moved forwardly by ground engaging wheels or tracks. The frame supports a hopper into which the paving material is dumped. The paving material is removed from the hopper and moved rearwardly by a pair of endless belt type feed conveyors, one on each side of the machine. The feed conveyors deposit the paving material in a transverse trough containing a pair of laterally extending spreader screws or augers. These augers spread the material out forwardly of a finishing screed which trails the augers. The finishing screed functions to screed and level the paving material.
Finishing machines of the type described are disclosed by the following U.S. Pat. Nos. 2,351,592, granted June 20, 1944 to Harry H. Barber; 2,589,256, granted Mar. 18, 1952, to Harold R. Horning; Re No. 25,275, granted Oct. 30, 1962 to Harold C. Pollitz; 3,453,929, granted July 8, 1969 to Harold C. Pollitz, Vernon L. Schrimper and Louis F. Fairchild; 3,537,363, granted Nov. 3, 1970, to George E. Long and Howard G. Anson; 3,678,817, granted July 25, 1972, to Earl D. Martenson and James J. Gebhardt, Jr.; 3,700,288, granted Oct. 24, 1972, to Donald R. Davin and Gary H. Beckley.
Paving machines of the type described which are known to be in use have feed conveyors and spreader augers which are mechanically coupled together and driven by single drive motors. They include a strike-off gate which is vertically movable and is raised or lowered for the purpose of varying the depth of the material which is deposited on the feed conveyors, to in this manner vary the quantity of material which is delivered from the hopper to the region forwardly of the screed.
Several of the aforementioned patents teach varying the feed rate by varying the drive speed of the feed conveyors and spreader augers. Some of such patents teach driving each feed conveyor and its spreader auger independently of the other feed conveyor and its spreader auger. Pollitz et al U.S. Pat. No. 3,453,939 proposes the use of manually controllable means for varying the speed of each feed conveyor and each spreader auger. Each feed conveyor and each spreader auger has its own hydraulic drive motor. The drive motors are independently controllable so that the drive speed of each feed conveyor can be varied relative to the drive speed of its spreader auger.
Pollitz, U.S. Pat. No. 25,275; Pollitz et al U.S. Pat. No. 3,453,939; Long U.S. Pat. No. 3,537,363 and Martenson et al. U.S. Pat. No. 3,678,817 disclose control systems for the feed conveyors and the spreader augers which include material level sensing units positioned at the sides of the machine, adjacent the outer ends of the augers. In the machines disclosed by Pollitz U.S. Pat. No. 25,275 and Pollitz et al U.S. Pat. No. 3,453,939, the sensors are in the nature of limit switches which sense only the presence of excess material and function to interrupt operation of the feed conveyor and the spreader screw on the side of the machine to which an excess of material has been delivered. Long U.S. Pat. No. 3,537,363 and Martenson et al U.S. Pat. No. 3,678,817 disclose automatic control systems for varying the drive speed of each feed conveyor and its spreader screw in response to changes in the depth of material sensed at the outboard end of a spreader screw.